Trophic and non-trophic interactions between macrophytes and macroinvertebrates in lowland streams

Through their form and functioning, aquatic macrophytes can have a great impact on the macroinvertebrate community in temperate lowland streams. Effects of macrophytes range from abiotic, such as the impact of growth form on water flow, to biotic, such as a macroinvertebrate food source. Although certain interactions between macrophytes and macroinvertebrate have been studied before, much is still unknown about the role of macrophytes within the aquatic food web. This thesis aims to further elucidate the role of trophic and non-trophic interactions between macrophytes and macroinvertebrates in temperate lowland streams, paying special attention to the macrophytes’ direct (e.g. direct consumption of living macrophytes and macrophyte-derived organic matter) and indirect (e.g. influence on other food sources, such as epiphytic algae and bacteria) role in the aquatic food web. Macrophytes were observed to influence the macroinvertebrate community through a variety of mechanisms. Macrophyte physical structure was found to influence habitat complexity and water flow velocity, both of which have an effect on the macroinvertebrate community. Furthermore, an increase in macrophyte complexity led to an increased epiphyton cover, an important food source for many herbivorous macroinvertebrates. However, the net effect of macrophytes on their epiphytic biofilm was mixed, due to the combined excretion of allelochemicals and nutrients. Stable isotope measurements revealed that certain macroinvertebrate taxa, expected to feed on epiphytic biofilm, were observed to assimilate macrophyte tissue. The fact that taxa of the scraper functional group, feeding close to the macrophyte leaf surface, were calculated to assimilate more macrophyte derived compounds than taxa classified as gatherers, feeding further away from the leaf surface, led to the hypothesis that accidental leaf erosion during grazing was the cause for the observed macrophyte consumption. Additionally, certain macroinvertebrate shredders were observed to directly consume macrophyte tissues, Potentially leading to a drastic reduction in macrophyte populations, especially when these are already subjected to other stressors. In addition to the consumption of living macrophytes, macroinvertebrate filter-feeders were also observed to consume macrophyte-derived organic matter, after its breakdown to fine particulate organic matter (FPOM). This consumption pattern was especially prevalent at the end of the growing season, when large amounts of macrophyte tissue entered the detrital food web. The observations from thesis indicate that macrophytes have a significant effect on the functioning of the aquatic systems in which they occur, and that this effect is broader than the purely structural role that is often focused upon.

Jaar van publicatie:2019

Trefwoorden:Doctoral thesis

Toegankelijkheid:Open